Small-Block Bolt-Ons - Chevys Gone Wild

Making a mundane two-barrel small-block into a spicy meatball

Dedicated engine builds are great fun, but more often than not theycreate as many questions as answers. For instance, building a 500hpsmall-block is extremely rewarding, especially if you get some seat timebehind the wheel of the monster. While the 500hp combination mightprovide impressive acceleration, not everyone is interested in that kindof top-end power. What does the torque curve look like and (moreimportantly) can it be improved or shifted to suit a different purpose,like towing for instance? Knowing that a dedicated small-block Chevybuildup can often create as many questions as answers, we decided totake a different approach for the readers of Super Chevy. In place of asingle-minded, small-block build up, we decided to cater to as manycombinations as possible given our limited dyno time. The one consistentcomponent in the equation was the four-bolt main short block provided byCoast High Performance. After purchasing the four-bolt truck motor froma local wrecking yard, I was fortunate enough to stumble upon not onlythe more desirable four-bolt block but also a short-block that seemed tobe in pretty decent shape internally. Basically I had a usable core thatwas the perfect starting point for a series of performance tests thatwould more than double the power output of the stock motor.

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The original four-bolt short-block was in decent shaped when removed,but was taken to Coast High Performance for a quick once over. The 350small-block was treated to 0.040-over forged flat-top pistons, forgedI-beam rods and the usual array of new rings and bearings.

As with any project, we needed an official starting point. In this casethat starting point would be a bone stock small-block 350 equipped witha two-barrel carb and intake (and matching air cleaner), stock heads,and cam and even the wretched factory cast-iron exhaust manifolds. Theidea was to start with the most basic of small-blocks, in its lowesthorsepower form. Why start with the lowly two-barrel motor? Believe itor not, there were a great many more two-barrel 350s offered by GM thanthe high-performance four-barrel versions. While the 350 will end upwith a set of aftermarket aluminum cylinder heads, a hydraulic rollercam, and racey single-plane intake, not everyone wants to take theircombination that far. What happens if you just want to replace yourtwo-barrel induction with a four-barrel Q-jet? These parts cost almostnothing at a bone yard, but they actually offer impressive gains overthe stock two-barrel. Ditto for a simple air cleaner swap or evensmall-tube headers. Rather than cater to the high-end enthusiasts, wedecided to cover the basics along the way.

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The original four-bolt short-block was in decent shaped when removed,but was taken to Coast High Performance for a quick once over. The 350small-block was treated to 0.040-over forged flat-top pistons, forgedI-beam rods and the usual array of new rings and bearings.

The first order of business was to get the short block prepped and readyfor action. The small-block 350 was taken to Coast High Performancewhere the four-bolt block was bored 0.040 over in preparation for a setof forged pistons and I-beam connecting rods along with the factory castcrank. The factory crank was deemed more than adequate for our intendedpower and rpm needs and was found to be in excellent shape, requiring nomachining whatsoever. After the forged flat-top pistons (with valvereliefs) and I-beam connecting rods were installed with a fresh set ofrings and bearings, or reciprocating assembly was ready for action. Allthe short-block needed was a new factory cam, since the previous ownerhad installed a mild RV cam. A trip to a local auto parts store resultedin a stock (180hp 307 and 350 applications) hydraulic flat-tappetcamshaft. For oil pump duties, we selected a Mellings standard-volumeoil pump and new pickup along with a hardened oil pump drive shaft. Theheavy-duty oil pump shaft was only a few bucks more, but well worth itwhen rebuilding any motor. A shaft failure means no oil pressure, whichin turn means no more engine or at the very least no bearings. After aliberal dose of Lucas Oil assembly lube and a once over with the torquewrench, the Coast High Performance four-bolt 350 short-block was readyfor cylinder heads.

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We also upgraded the timing chain to double roller status.

When purchased from the original owner, the 350 core motor was alsoequipped with a set of 882 cast-iron cylinder heads. To put our heads ingood working order, they were taken to Power Heads in Fullerton,California. While the motor was running when removed, the heads weretreated to a simple (matching the factory) valve job, reamed guides anda fresh set of factory valve springs. Unfortunately for us, one of theoriginal 882 heads was cracked, not uncommon given the age and usage.Fortunately for us, the guys at Power Heads came to the rescue not onlywith a replacement casting, but also a set of ported heads for ourtesting. Obviously porting your existing heads is an alternative topurchasing expensive aftermarket heads. Power Heads went to work on the882 castings, treating them to a full port job (intake, exhaust, andchambers) designed to work with the larger 2.02 intake and 1.60 exhaustvalves. The heads were finished up with a performance three-angle valvejob. Before porting, the heads were surfaced to ensure proper sealing.The heads were not milled to increase the compression ratio, just aminimal cut to produce a straight, level surface. The pushrods andfactory stamped steel rockers were reused.

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Our original 882 heads were freshened up by Power Heads in Fullerton,California. Power heads also supplied the ported version complete with a2.02/1.60 valve package.

Before we could start our testing, it was necessary to do a littlewrecking yard rummaging. Since our 350 core motor was originallyequipped with a factory four-barrel Q-Jet intake and carb, we wentlooking to secure (of all things) a stock cast-iron two-barrel intake,carb and air cleaner assembly. Not a hot item in the wrecking yards,even the workers laughed at us when we brought it up to pay the askingprice of $20. While we all take for granted that every carburetor istopped with a free-flowing performance filter, the reality is that thereare a great many factory air cleaners still running around and we wantedto demonstrate the effectiveness of a good filter system. We enlistedthe aide of Sean Murphy Induction (SMI) to make sure that both the 2GRochester and Q-Jet were in good working condition. Though we had nointention of keeping them on the motor, we wanted to demonstrate thepower potential of the combination without fear that either carb waspoorly tuned. Both SMI carbs performed so well that it was a shame toremove them, though the after market carbs did show major powerimprovements.

Before attempting to run either of the factory intakes on our freshlyrebuilt 350, they were in need of a good cleaning. The first step was totake them both to a local machine shop for bead blasting. Naturally wehated treating the factory cast-iron intakes to such expensivepampering, we just did not want them to deposit all the years of carbonbuildup (and now beading blasting material) into our new motor. Afterblasting, we also took the opportunity to grind the rivets securing theoil splash plate located on the under side of each intake. It was a goodthing we did, as both bead blasting material and years of carbon buildup had made a new home under the plate. The bead blasting and plateremoval were followed up by a good cleaning in the solvent tank. Alittle touch of Chevy orange paint and our (heavy) cast-iron intakeswere ready for dyno action. We contemplated blasting the factory cast-iron exhaust manifolds, but they were left in as-delivered conditionsince they would be quickly replaced by long-tube headers duringtesting.

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Replacing the factory single-snorkel filter assembly with an openelement version from Comp Cams improved the power output to 241 hp.

As usual, all of the engine dyno testing was performed at WestechPerformance ( SuperFlow 9010 engine dyno). Once assembled, the 350 testmotor was installed on the dyno and filled with a conventional 10W-30from Lucas Oil. After initial start up, we quickly adjusted the MSDdistributor (though the stock HEI worked fine as well) to achieve 36degrees of total timing at wide-open throttle. We relied on an InnovateLM-2 air/fuel meter to help tune the carburetors. Our break-in procedure(for the cam, lifters, rings and bearings) consisted of running themotor at varying loads (the Super Flow actually had a computerizedbreak-in procedure) for 25-30 minutes. Our standard volume Mellings oilpump was doing its job by providing a minimum oil pressure of 50 psi atany speed above 1,500 rpm. After the break in procedure, we ran ProjectChevys Gone Wild in stock trim (from the stock two-barrel air cleanerdown through the stock exhaust manifolds (through a dual exhaust).Equipped as such, the bone-stock Chevy 350 produced 229 hp at 4,600 rpmand 350 lb-ft of torque at just 2,900 rpm. Not exactly a high-rpmscreamer, but the two-barrel motor could sure be used for towing giventhe impressive low-speed torque production.

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The next step was to improve the exhaust side of the equation byinstalling a set of 1 5/8-inch Flow Tech headers. Given the relativelylow power output of the motor at this stage, the stock exhaust manifoldsdid not represent much of a restriction. Despite the low power output ofthe test motor, the headers improved the peak power numbers to 248 hpand 366 lb-ft of torque.

The 229hp small-block was certainly designed with low-speed torqueproduction in mind. Though torque production exceeded 350 lb-ft out to3,300 rpm, the torque curve fell off rapidly thereafter. A motor likethis would feel snappy at part throttle, giving the illusion ofperformance, but with only 229 hp, would certainly fail to deliver uponthose promises. On the plus side, the motor (with proper gearing) wouldlikely deliver decent fuel economy and years of trouble-free service.Our list of modifications started out small, the first being a simpleair cleaner test. I can remember swapping out the air cleaner on my veryfirst car (a '70 split-bumper Camaro RS) for a chrome (which isobviously faster) open-element performance filter. The sound difference(if not the actual performance) was certainly noticeable on mytwo-barrel small-block, but what would the dyno say about this one?Replacing the stock single-snorkel filter with an open element versionfrom Comp Cams resulted in a jump in power from 229 hp to 241 hp (seegraph 1). The new filter resulted in a drop in manifold vacuum (at WOT)of one full inch (from 5.5 inches down to 4.5 inches), a sure sign thatthe stock filter assembly was a restriction.

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Knowing that the two-barrel intake and carb were restricting thesmall-block, we installed a factory four-barrel intake and Q-Jet carb.

After the simple filter upgrade, we started to get a little moreadventurous, first with the exhaust system and then again with theinduction system. First off, we replaced the stock cast-iron exhaustmanifolds with Flow Tech long-tube headers. Breathing into the same dual('70-'81 Camaro system from Hooker) exhaust, the headers improved thepower output from 241 hp and 359 lb-ft of torque to 248 hp and 366 lb-ftof torque (see graph 2). Given the mild state of tune, we didn't reallyexpect too much from the headers at this point. Next up we replaced thecast-iron two-barrel carb and intake with a factory (the original forthe motor) four-barrel intake and Q-Jet carb. Cast-iron intakes, headsand exhaust manifolds should all be illegal, strictly from a weightstandpoint. Despite its heft and factory origins, the four-barrel Q-Jetinduction improved the power output from 248 hp and 366 lb-ft of torqueto 278 hp and 385 lb-ft of torque (see graph 3). Not just in peaknumbers, the four-barrel carb and intake improved the power outputsubstantially from 3,000 rpm to 5,000 rpm, with little to no trade offin low-speed torque (maybe 1-2 lb-ft at 2,300 rpm). So far, everythingwas going according to plan.

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The new induction system reduced the manifold vacuum under WOT byseveral inches and upped the power output to 278 hp and 385 lb-ft oftorque.

Having had our daily dosage of iron, off came the stock four-barrelQ-Jet intake and on went an (oh-so-light) aluminum 8004 intake fromWeaind. The new intake (using the same 750-cfm Q-Jet carb) resulted in ajump in peak power from 278 hp and 385 lb-ft of torque to 287 hp and 372lb-ft of torque (see graph 4). We found out that it is tough to beat thestock Q-Jet intake down low and that the power gains offered from 4,000rpm on up cost some torque production near 3300 rpm. Here is where thepower gains started to get serious. After the installation of the Weiand8004 intake, of came the stock 882 heads and auto-parts store specialfactory camshaft. These stock components were replaced by the set ofported (and big-valve) 882 castings from Power Heads along with a mild(and emissions legal) PE246 cam from Comp Cams. The dual-pattern PE246offered 0.429/0.438 lift split, a 203/212 duration split and a110-degree lobe separation angle. Basically one step up from a stockcam, the PE 246 combined with the ported 882 heads to produce animpressive power gain. The head and cam combo increased the power outputof the 350 test motor literally everywhere, from 2500 rpm all the way to5600 rpm (the new cam and heads allowed us to rev the motor higher). Thepeak numbers with the new hydraulic flat-tappet cam and ported heads nowstood at 340 hp and an even 400 lbs. ft. of torque (see graph 5).

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We'd install the Weiand 8004 aluminum intake just to get rid of theheavy cast-iron factory Q-Jet intake, but the icing on the cake was ajump in power from 278 hp to 287 hp.

We were plenty impressed by the current combination, since the motor wassporting the smallest cam in the Comp Cams catalog along with a $100after market intake and a set of ported stock heads. The motor idledalmost like a stocker while offering even better low-speed torque and aton more high-rpm power. Torque production from the 350 small-block nowexceeded 350 lbs. ft. from below 2500 rpm all the way to 5100 rpm. Thefinal modification for part one of Chevys Gone Wild was the installationof an Edelbrock Performer RPM Air Gap and 650 Might Demon carburetor.Though a dual-plane like the Weiand 8004, the Air Gap intake offeredgreater cross section for improved power production. Naturally we wereconcerned about a loss of low-speed power, since the previouscombination worked so well, but our fears were unfounded. Installationof the BG carb and Edelbrock intake not only upped the peak power outputfrom 340 hp and 400 lb-ft of torque to 364 hp and 422 lb-ft of torque(see graph 6), but did so without any trade of in low-speed torque (evenas low as 2,400 rpm). So far, we had managed to improve the peak powernumbers of the 350 small-block by nearly 200 hp (229 hp vs 422 hp) andnearly 75 lb-ft of torque (350 lb-ft vs 422 lb-ft). Check back with usnext month when we step up to not one but two different sets of aluminumheads, a couple of different cam profiles and even a single-planeintake.

Graph 1: Stock Air Cleaner vs Comp Cams Open Element

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Graph 1: Stock Air Cleaner vs Comp Cams Open Element

For our first test, we replaced the stock single-snorkel air filterassembly (with new paper filter element) with a composite unit from CompCams. The Composite air filter assembly was designed to mount on our 2GRochester two-barrel and provided an unobstructed flow of air into thecarburetor. Data logging showed that the new air filter dropped themanifold vacuum (surefire evidence of an airflow restriction) from 5.5inches (with the stock filter assembly) down to 4.5 inches. Thereduction in manifold vacuum brought with it an increase in power, inthis case from 229 hp and 350 lb-ft of torque to 241 hp and 359 lb-ft oftorque.

Graph 2: Stock Exhaust Manifolds vs Flow Tech Headers

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Graph 2: Stock Exhaust Manifolds vs Flow Tech Headers

With the small-block only producing 241hp, we didn't really expect tomuch of a power gain from replacing the cast-iron exhaust manifolds withthe Flow Tech headers, but we knew they would show huge dividends laterin our testing. The headers were installed using the same Hooker2.5-inch exhaust system, minus the 90-degree bends used with the stockmanifolds. Running the long-tub headers resulted in an increase in peakpower from 241 hp and 359 lb-ft of torque to 248 hp and 366 lb-ft oftorque. Note that the headers improved power production across the revrange-always a good sign.

The power gains started to get serious with the introduction of thefactory cast-iron Q-Jet intake and matching 750-cfm (SMI rebuilt) Q-Jetcarb. The peak numbers were up from 248 hp and 366 lb-ft of torque to287 hp and 372 lb-ft of torque. The four-barrel induction reduced themanifold vacuum down to 0.5 inches, which explains the impressive powergain. Check out the solid gain of 30-35 lb-ft of torque from 3,200 rpmto 5,000 rpm. You'd certainly be able to feel a power gain of thismagnitude.

Graph 4: Q-Jet Cast Iron Intake vs Weiand 8004 Aluminum Intake

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Graph 4: Q-Jet Cast Iron Intake vs Weiand 8004 Aluminum Intake

This next test illustrated just how difficult it is to better thefactory cast-iron intake at low rpm. Installation of the Weaind 8004aluminum improved the peak power from 278 hp to 287, but peak torqueproduction was down from 385 lb-ft. to 372 lb-ft. In fact, the entirecurve was down from 2,200 rpm to 4,100 rpm, though there was very littledifference down below 3,000 rpm. This test is classis example of why Iinclude full graphs with all of my testing. Judging by just the peakhorsepower numbers, you'd be accurate to say the Weiand improved thepower output. Judging by the peak torque numbers, you'd be equallyaccurate to say the Weiand lost power. Which is right? Only by viewingthe entire curve can we see that both statements are correct.

While the torque production of this small-block was always impressive,we were getting tired of seeing the peak power output climb oh-so-slowlytoward the 300hp mark. That situation quickly rectified itself after theinstallation of the next performance components. Off came the stock 882heads and 180-hp factory hydraulic flat-tappet cam an in their placewent an emissions legal PE246 cam and a set of ported (and big-valve)882 heads from Power Heads. Obviously the combination worked welltogether, as the new cam and ported stock heads improved the peak poweroutput from 287 hp to a whopping 340 hp. The heads and cam improvedhorsepower production by as much as 60 hp and 63 lb-ft of torque. Thetorque production took a healthy jump as well, from 372 lb-ft to an even400 lb-ft, with substantial torque improvements even down at 2,500 rpm.

The final test for part one of Chevy Gone Wild involved replacing thecurrent induction system with an Edelbrock Performer RPM Air Gap andBarry Grant 650 Mighty Demon carb. Off came the Weiand 8004 and stockQ-Jet and on went the new components. The motor responded very well tothe new performance induction system, as the peak power numbers jumpedfrom 340 hp and 400 lb-ft of torque to 364 hp and 422 lb-ft of torque.Torque production on the 355 (0.040 over) small-block now exceeded 400lb-ft from 2,900 rpm to 4,700 rpm. We were pleasantly surprised that thehigh-performance induction system lost no power to the Weaind and Q-Jeteven down as low as 2500 rpm. With 364 hp and 422 lb-ft of torque, wehave come a long way from the 229 hp and 350 lb-ft of the originaltwo-barrel test motor, but there is even more power to be had from thissmall-block in the next issue.

After witnessing the kind of power Edelbrock made with their 383 crate engine, we were optimistic on building our very own 383 chevy short block and for our foundation we got a 350 small block from Powerhouse Engine Components. - Super Chevy Magazine » Read More